1. Field of the Invention
This invention relates in general to earth boring and in particular to means for positioning the mast of an earth boring machine.
2. Description of the Prior Art
In the earth boring arts, hydraulically operated shaft drilling machines are known. (See U.S. Pat. No. 3,695,363, "Rotary Shaft Drilling Apparatus," Joseph L. Kelly, Jr., Oct. 3, 1972.) Such machines have masts that are raised, lowered and selectively positioned to drill holes at various angles. Hydraulic cylinders move a drilling assembly along the mast, and the assembly uses a hydraulically powered swivel to rotate pipe which supports the drill bit. One technique for positioning the mast is shown in U.S. Pat. No. 3,563,332, "Earth Boring Machine Positioning System," issued to James W. Young, Feb. 16, 1971. In general this patent teaches a system for positioning the mast by attaching a fixed linkage between the base and drilling assembly, which when moved linearly by the hydraulic cylinders changes the angular position of the mast.